In typical fire tube cutting operations, a fire tube is placed in a retained position and cut by a cutting tool applied to the outside circumference of the tube at the position where the cutting is desired. Although this operation might be satisfactory for fire tubes which are easily movable, a problem arises with fire tubes already installed e.g., one such situation involves fire tubes which are installed in a heat exchange system. The location of the fire tubes in such cases may be such that circumferential cutting of the tube around its outer surface is either impossible, impractical, or undesirable.
There are tools available in the prior art which are capable of performing the desired operation but suffer from certain drawbacks. The specific use envisioned and illustrated in this particular case favors the use of a well known tool which is one that performs a "chipless" cutting operation as opposed to the type of tool that presents a tool bit to the surface similar to that used in a lathe or similar chip making metal cutting operation. The operational and housekeeping advantages of the "chipless" tube cutter outweigh the design and manufacturing problems associated with tools of this type. One of the causes of difficulties has been that the force necessary to enable the cutting wheel to penetrate into and cut through the tube wall is many times greater than that required to rotate the tool carrying the cutter. Compounding of the difficulty is occasioned because the cutter force must be applied in a direction at right angles to the axis of the tool and since there are physical limitations on the size of the components by virtue of the necessity of operating inside of the tube to be cut, excess stress and wear has been experienced by certain elements of these tools.
Moreover, typical tube cutting operations, such as that possible with the devices disclosed in U.S. Pat. Nos. 1,499,429; 1,789,572; and 2,028,578, generate such substantial great torque loads that a two man operation is required for safety purposes. In addition, such operations often involve single rotation cuttings which require excessive torques that in turn result in damage to or roughening of the resulting tube edge.
Prior art tools have also required two separate power inputs to perform the desired operation. This required the inputs to be made in sequence and thus add to the time required to cut a tube and/or use two men. The latter practice would decrease the time required but often led to premature tool breakdown because of the difficulty of properly synchronizing their efforts.
I have invented an apparatus and a method for cutting tubes which overcomes the above-noted limitations of the prior art.